Mask blank, phase shift mask, and method for manufacturing semiconductor device

ABSTRACT

Provided is a mask blank for a phase shift mask including an etching stopper film. A mask blank has a structure where a transparent substrate has layered thereon an etching stopper film and a phase shift film in this order, in which the phase shift film contains silicon and oxygen, in which the phase shift film has a refractive index n 1  of 1.5 or more for light of 193 nm wavelength and an extinction coefficient k 1  of 0.1 or less for light of 193 nm wavelength, in which the etching stopper film has a refractive index n 2  of 2.6 or more for light of 193 nm wavelength and an extinction coefficient k 2  of 0.4 or less for light of 193 nm wavelength, and the refractive index n 2  and the extinction coefficient k 2  satisfy at least one of k 2 ≤[(−0.188×n 2 )+0.879] and k 2 ≤[(2.75×n 2 )−6.945].

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2019/005030, filed Feb. 13, 2019, which claims priority toJapanese Patent Application No. 2018-167622, filed Feb. 27, 2020, andthe contents of which is incorporated by reference.

TECHNICAL FIELD

This disclosure relates to a mask blank and a phase shift maskmanufactured using the mask blank. This disclosure further relates to amethod of manufacturing a semiconductor device using the phase shiftmask.

BACKGROUND ART

Generally, in a manufacturing process of a semiconductor device,photolithography is used to form a fine pattern. A number of transfermasks are usually used to form the pattern. Particularly, in forming afine pattern, a phase shift mask with an enhanced transfer performance,mainly resolution, by using phase difference of light is often used.Further, in order to miniaturize a pattern of a semiconductor device, inaddition to improvement of a transfer mask represented by a phase shiftmask, it is necessary to shorten a wavelength of an exposure lightsource used in photolithography. Thus, shortening of wavelength has beenadvancing recently from the use of KrF excimer laser (wavelength 248 nm)to ArF excimer laser (wavelength 193 nm) as an exposure light sourceused in the manufacture of a semiconductor device.

The types of these mask blanks for a phase shift mask include a shifteroverlaid Levenson type, a shifter underlying Levenson type, a half tonetype, etc. For example, Patent Document 1 discloses a shifter overlaidLevenson type mask blank. This mask blank has an etching stopper layerbetween a transparent substrate and a phase shifter layer fordry-etching the phase shifter layer provided on a transparent substrate.This etching stopper layer is made of a layer including hafnium oxide.

Further, Patent Document 2 discloses a mask blank for a chromeless phaseshift mask, in which a substrate that is transparent to an exposurelight is provided with a dug-down portion to control the phase of atransmitting light. A light shielding film provided in a part adjacentto the dug-down portion of the substrate or in the peripheral part ofthe substrate includes a film A including a material which can be etchedin an etching process using etching gas mainly including fluorine-basedgas.

PRIOR ART PUBLICATIONS Patent Documents [Patent Document 1] Japan PatentNo. 3301556 [Patent Document 2] Japanese Patent Application Publication2007-241136 SUMMARY OF THE INVENTION Problems to be Solved by theInvention

In the case of a chromeless phase shift mask in which a substrate itselftransparent to an exposure light is provided with a dug-down portion asdescribed in Patent Document 2, each dug-down portion of the phase shiftmask is simultaneously formed by dry-etching the substrate. In theconventional dry etching in which a dug-down portion is formed in atransparent substrate, it is difficult to detect an etching end pointunlike the case where a phase shift film provided on a transparentsubstrate is patterned by etching. Even if a bottom shape and depth of apattern of each dug-down portion in a phase shift mask are controlled bythe etching time, they are affected by a micro-trench phenomenon, amicro-loading phenomenon, etc. Therefore, it is not easy to control abottom shape and depth of each dug-down portion by dry etching.

On the other hand, an investigation is being made on a mask blank for achromeless phase shift mask with a configuration where an etchingstopper film is provided on a substrate, and a phase shift filmincluding silicon and oxygen and having substantially the sametransmittance as that of a transparent substrate is provided on theetching stopper film. When a phase shift mask is manufactured, this maskblank is desired to generate a phase shifting effect between an exposurelight that passes through a portion of the etching stopper film wherethe phase shift film exists (non-dug-down portion) and an exposure lightthat passes through a portion of the etching stopper film where thephase shift film does not exist (dug-down portion).

In the case of a chromeless phase shift mask, generation of a high phaseshifting effect is desired since an exposure light pattern is formedonly by the phase shifting effect that generates between an exposurelight that passed through the non-dug-down portion and an exposure lightthat passed through the dug-down portion. Therefore, it is desired thatthe etching stopper film has a transmittance of 80% or more with respectto an ArF exposure light in a stacked structure of the etching stopperfilm and a phase shift film formed thereon.

The etching stopper film is left in both the patterned portion (dug-downportion) and the unpatterned portion (non-dug-down portion) of thetransparent portion of the phase shift film. Decrease in transmittanceof an exposure light in the transparent portion of the phase shift maskleads to decrease in an integrated amount of irradiation of an exposurelight to a transfer object per unit time. Therefore, it is necessary toincrease the exposure time, which leads to decrease in throughput of anexposure transfer step in a manufacture of a semiconductor device. Fromthis viewpoint, the etching stopper film is desired to have atransmittance of 80% or more with respect to an ArF exposure light in astacked structure with the phase shift film formed thereon.

The etching stopper film used in the phase shift photomask blankdescribed in Patent Document 1 has a transmittance at an i-line (365 nm)of a mercury lamp having a relatively long wavelength and at awavelength (248 nm) of a KrF excimer laser. However, the transmittancewas insufficient in a wavelength of an ArF excimer laser used forforming a finer pattern.

In addition, in order to improve inspection accuracy of a pattern formedin a phase shift film, a wavelength of an inspection light has also beenshortened. In recent years, defect inspection of a pattern using aninspection light of 193 nm wavelength, which is equivalent to that of anArF excimer laser, has also been performed. In order to inspect apattern defect with high accuracy using such a short wavelengthinspection light, it is desired that a contrast ratio calculated bydividing a reflectance of an etching stopper film alone to a light of193 nm wavelength by a reflectance of a stacked structure of an etchingstopper film and a phase shift film to a light of 193 nm wavelength is1.5 or more.

This disclosure was made to solve the conventional problem describedabove. Namely, an aspect of this disclosure is to provide a mask blankfor a phase shift mask in which, in a mask blank having a structure inwhich a transparent substrate has stacked thereon an etching stopperfilm and a phase shift film in this order, the mask blank has an etchingstopper film having a high transmittance to an ArF exposure light andcan obtain a high contrast ratio to an inspection light of 193 nmwavelength equivalent to that of an ArF exposure light. A further aspectis to provide a phase shift mask manufactured using this mask blank. Yetanother aspect of this disclosure is to provide a method ofmanufacturing a semiconductor device using such a phase shift mask.

Means for Solving the Problem

For solving the above problem, this disclosure includes the followingconfigurations.

(Configuration 1)

A mask blank having a structure where a transparent substrate hasstacked thereon an etching stopper film and a phase shift film in thisorder,

in which the phase shift film is made of a material containing siliconand oxygen,

in which the phase shift film has a refractive index n₁ of 1.5 or moreto a light of 193 nm wavelength and an extinction coefficient k₁ of 0.1or less to a light of 193 nm wavelength, and

in which the etching stopper film has a refractive index n₂ of 2.6 ormore to a light of 193 nm wavelength and an extinction coefficient k₂ of0.4 or less to a light of 193 nm wavelength, and the refractive index n₂and the extinction coefficient k₂ satisfy any of (Condition 1) and(Condition 2).

k ₂≤−0.188×n ₂+0.879  (Condition 1)

k ₂>−0.188×n ₂+0.879 and k ₂≤2.750×n ₂−6.945  (Condition 2)

(Configuration 2)

The mask blank according to Configuration 1, in which the etchingstopper film has the refractive index n₂ of 3.1 or less.

(Configuration 3)

The mask blank according to Configuration 1 or 2, in which the etchingstopper film has the extinction coefficient k₂ of 0.05 or more.

(Configuration 4)

The mask blank according to any of Configurations 1 to 3, in which thephase shift film has the refractive index n₁ of 1.6 or less.

(Configuration 5)

The mask blank according to any of Configurations 1 to 4, in which thetransparent substrate has a refractive index n₃ of 1.5 or more and 1.6or less to a light of 193 nm wavelength, and an extinction coefficientk₃ of 0.1 or less to a light of 193 nm wavelength.

(Configuration 6)

The mask blank according to any of Configurations 1 to 5, in which astacked structure of the etching stopper film and the phase shift filmhas a transmittance of 80% or more to a light of 193 nm wavelength.

(Configuration 7)

The mask blank according to any of Configurations 1 to 6, in which acontrast ratio calculated by dividing a front surface reflectance of theetching stopper film alone to a light of 193 nm wavelength by a frontsurface reflectance of a stacked structure of the etching stopper filmand the phase shift film to a light of 193 nm wavelength is 1.5 or more.

(Configuration 8)

The mask blank according to any of Configurations 1 to 7, in which theetching stopper film is made of a material containing hafnium andoxygen.

(Configuration 9)

The mask blank according to any of Configurations 1 to 8, in which theetching stopper film is formed in contact with a main surface of thetransparent substrate.

(Configuration 10)

The mask blank according to any of Configurations 1 to 9, in which theetching stopper film has a thickness of 1 nm or more and 4 nm or less.

(Configuration 11)

The mask blank according to any of Configurations 1 to 10, in which thephase shift film has a function to generate a phase difference of 150degrees or more and 210 degrees or less between a light of 193 nmwavelength that transmitted through the phase shift film and a light of193 nm wavelength that transmitted through the air for a same distanceas a thickness of the phase shift film.

(Configuration 12)

The mask blank according to any of Configurations 1 to 11 including alight shielding film on the phase shift film.

(Configuration 13)

The mask blank according to Configuration 12, in which the lightshielding film is made of a material containing chromium.

(Configuration 14)

A phase shift mask having a structure where a transparent substrate hasstacked thereon an etching stopper film and a phase shift film having aphase shift pattern in this order,

in which the phase shift film is made of a material containing siliconand oxygen,

in which the phase shift film has a refractive index n₁ of 1.5 or moreto a light of 193 nm wavelength and an extinction coefficient k₁ of 0.1or less to a light of 193 nm wavelength, and

in which the etching stopper film has a refractive index n₂ of 2.6 ormore to a light of 193 nm wavelength and an extinction coefficient k₂ of0.4 or less to a light of 193 nm wavelength, and the refractive index n₂and the extinction coefficient k₂ satisfy any of (Condition 1) and(Condition 2).

k ₂≤−0.188×n ₂+0.879  (Condition 1)

k ₂>−0.188×n ₂+0.879 and k ₂≤2.750×n ₂−6.945  (Condition 2)

(Configuration 15)

The phase shift mask according to Configuration 14, in which the etchingstopper film has the refractive index n₂ of 3.1 or less.

(Configuration 16)

The phase shift mask according to Configuration 14 or 15, in which theetching stopper film has the extinction coefficient k₂ of 0.05 or more.

(Configuration 17)

The phase shift mask according to any of Configurations 14 to 16, inwhich the phase shift film has the refractive index n₁ of 1.6 or less.

(Configuration 18)

The phase shift mask according to any of Configurations 14 to 17, inwhich the transparent substrate has a refractive index n₃ of 1.5 or moreand 1.6 or less to a light of 193 nm wavelength, and an extinctioncoefficient k₃ of 0.1 or less to a light of 193 nm wavelength.

(Configuration 19)

The phase shift mask according to any of Configurations 14 to 18, inwhich a stacked structure of the etching stopper film and the phaseshift film has a transmittance of 80% or more to a light of 193 nmwavelength.

(Configuration 20)

The phase shift mask according to any of Configurations 14 to 19, inwhich a contrast ratio calculated by dividing a front surfacereflectance of the etching stopper film alone to a light of 193 nmwavelength by a front surface reflectance of a stacked structure of theetching stopper film and the phase shift film to a light of 193 nmwavelength is 1.5 or more.

(Configuration 21)

The phase shift mask according to any of Configurations 14 to 20, inwhich the etching stopper film is made of a material containing hafniumand oxygen.

(Configuration 22)

The phase shift mask according to any of Configurations 14 to 21, inwhich the etching stopper film is formed in contact with a main surfaceof the transparent substrate.

(Configuration 23)

The phase shift mask according to any of Configurations 14 to 22, inwhich the etching stopper film has a thickness of 1 nm or more and 4 nmor less.

(Configuration 24)

The phase shift mask according to any of Configurations 14 to 23, inwhich the phase shift film has a function to generate a phase differenceof 150 degrees or more and 210 degrees or less between a light of 193 nmwavelength that transmitted through the phase shift film and a light of193 nm wavelength that transmitted through the air for a same distanceas a thickness of the phase shift film.

(Configuration 25)

The phase shift mask according to any of Configurations 14 to 24including a light shielding film having a light shielding pattern with alight shielding band on the phase shift film.

(Configuration 26)

The phase shift mask according to Configuration 25, in which the lightshielding film is made of a material containing chromium.

(Configuration 27)

A method of manufacturing a semiconductor device including the step ofusing the phase shift mask according to any of Configurations 14 to 26and exposure-transferring a pattern on the phase shift mask in a resistfilm on a semiconductor substrate.

Effect of the Invention

The mask blank of this disclosure has a structure where a transparentsubstrate has stacked thereon an etching stopper film and a phase shiftfilm in this order, in which the phase shift film includes a materialcontaining silicon and oxygen, in which the phase shift film has arefractive index n₁ of 1.5 or more to a light of 193 nm wavelength andan extinction coefficient k₁ of 0.1 or less to a light of 193 nmwavelength, in which the etching stopper film has a refractive index n₂of 2.6 or more to a light of 193 nm wavelength and an extinctioncoefficient k₂ of 0.4 or less to a light of 193 nm wavelength, and therefractive index n₂ and the extinction coefficient k₂ satisfy any of(Condition 1) and (Condition 2).

k ₂≤−0.188×n ₂+0.879  (Condition 1)

k ₂>−0.188×n ₂+0.879 and k ₂≤2.750×n ₂−6.945  (Condition 2)

According to this disclosure, a mask blank for a phase shift mask can beprovided, which has an etching stopper film having a high transmittanceto an ArF exposure light of 193 nm wavelength and which can obtain ahigh contrast ratio to an inspection light of 193 nm wavelength.Accordingly, a light of 193 nm wavelength includes an ArF exposure lightand an inspection light of 193 nm wavelength that is equivalent to thatof the ArF exposure light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a configuration of the maskblank of the first embodiment of this disclosure.

FIG. 2 is a cross-sectional view showing a configuration of the phaseshift mask according to the first embodiment of this disclosure.

FIGS. 3A-3C are schematic cross-sectional views showing a manufacturingprocess of the phase shift mask according to the first embodiment ofthis disclosure.

FIG. 4 shows the relationship between a refractive index n₂ and anextinction coefficient k₂ and a minimum film thickness d of an etchingstopper film satisfying a front surface reflection contrast ratio of1.5, and the relationship between a refractive index n₂ and anextinction coefficient k₂ (k₂ ranging between 0.20 and 0.40) and amaximum film thickness d of an etching stopper film satisfying atransmittance of 80%, both relationships derived from the simulationresult.

FIG. 5 shows the relationship between a refractive index n₂ and anextinction coefficient k₂ (k₂ ranging between 0.20 and 0.40) and aminimum film thickness d of an etching stopper film satisfying a backsurface reflection contrast ratio of 1.5 derived from the simulationresult.

FIG. 6 shows the relationship between a refractive index n₂ and anextinction coefficient k₂ and a minimum film thickness d of an etchingstopper film satisfying a front surface reflection contrast ratio of1.5, and the relationship between a refractive index n₂ and anextinction coefficient k₂ (k₂ ranging between 0.05 and 0.40) and amaximum film thickness d of an etching stopper film satisfying atransmittance of 80%, both relationships derived from the simulationresult.

FIG. 7 shows the relationship between a refractive index n₂ and anextinction coefficient k₂ (k₂ ranging between 0.05 and 0.40) and aminimum film thickness d of an etching stopper film satisfying a backsurface reflection contrast ratio of 1.5 derived from the simulationresult.

EMBODIMENT FOR CARRYING OUT THE INVENTION

First, the proceeding that has resulted in the completion of thisdisclosure is described. The inventors of this disclosure diligentlystudied to obtain a mask blank for a phase shift mask, in which anetching stopper film and a phase shift film of a mask blank formanufacturing a CPL mask have a high transmittance of 80% or more to anArF exposure light, and which has an etching stopper film that canobtain a high contrast ratio of 1.5 or more to an inspection light of193 nm wavelength that is equivalent to that of the ArF exposure light.

In a mask blank having a structure in which a transparent substrate hasstacked thereon an etching stopper film and a phase shift film in thisorder, the phase shift film includes a material containing silicon andoxygen, and its refractive index n₁, extinction coefficient k₁, and filmthickness are restricted in terms of functions as a CPL mask. Therefore,it is necessary to control a refractive index n₂ and an extinctioncoefficient k₂ of the etching stopper film within a predetermined range.

The inventors focused herein on the relationship between a maximum filmthickness d of an etching stopper film and a refractive index n₂ and anextinction coefficient k₂ of an etching stopper film in order to satisfythe condition that a stacked structure of an etching stopper film and aphase shift film has a transmittance of 80% or more to a light of 193 nmwavelength, and carried out an optical simulation on an etching stopperfilm and a phase shift film. In the optical simulation, a maximum filmthickness d of an etching stopper film when a transmittance is 80% iscalculated while the values of a refractive index n₂ and an extinctioncoefficient k₂ of the etching stopper film are changed respectively inthe range between 2.6 and 3.1 for the refractive index n₂ and between0.05 and 0.40 for the extinction coefficient k₂. The phase shift filmherein had a film thickness of 177 (nm), a refractive index n₁ of 1.56,and an extinction coefficient k₁ of 0.00.

Thereafter, the relationship between a refractive index n₂ and anextinction coefficient k₂, and a maximum film thickness d of the etchingstopper film was organized based on the simulation result. FIGS. 4 and 6show the relationship between a refractive index n₂ and an extinctioncoefficient k₂, and a maximum film thickness d of the etching stopperfilm satisfying a transmittance of 80%.

Given below are the relational equations for a refractive index n₂ andan extinction coefficient k₂ of the etching stopper film satisfying atransmittance of 80% when maximum film thicknesses d of the etchingstopper film are 2.5 nm and 3.0 nm, respectively, as shown in FIGS. 4and 6.

k ₂=−0.156n ₂+0.859 (maximum film thickness d=2.5 nm)

k ₂=−0.188n ₂+0.879 (maximum film thickness d=3.0 nm)

Thus, it was found that there is a negative correlation between arefractive index n₂ and an extinction coefficient k₂ on the etchingstopper film satisfying a transmittance of 80%.

Further, the inventors focused on the relationship between a minimumfilm thickness of an etching stopper film and a refractive index n₂ andan extinction coefficient k₂ of an etching stopper film in order tosatisfy a front surface reflection contrast ratio of 1.5 and a backsurface reflection contrast ratio of 1.5, and carried out an opticalsimulation on an etching stopper film and a phase shift film. The rangesof a refractive index n₂ and an extinction coefficient k₂, a filmthickness of the phase shift film, a refractive index n₁, and anextinction coefficient k₁ in the optical simulation are the same asthose in the above-described simulation on the transmittance.

Thereafter, based on the simulation result, the relationship between arefractive index n₂ and an extinction coefficient k₂, and a minimum filmthickness d of an etching stopper film satisfying a front surfacereflection contrast ratio of 1.5 and a back surface reflection contrastratio of 1.5 was organized, respectively. FIGS. 4 and 6 show approximatecurves when minimum film thicknesses d of the etching stopper film are2.0 nm, 2.5 nm, and 3.0 nm, which satisfy a front surface reflectioncontrast ratio of 1.5. Further, FIGS. 5 and 7 show approximate curveswhen minimum film thicknesses d of the etching stopper film are 2.0 nmand 2.5 nm, which satisfy a back surface reflection contrast ratio of1.5. In the range of a refractive index n₂ and an extinction coefficientk₂ shown in FIGS. 4 to 7, the value of a minimum film thickness dsatisfying a back surface reflection contrast ratio of 1.5 is alwayssmaller than the value of a minimum film thickness d satisfying a backsurface reflection contrast ratio of 1.5. From these results, it wasfound that a back surface reflection contrast ratio of 1.5 can besatisfied by setting a minimum film thickness d of an etching stopperfilm to satisfy a front surface reflection contrast ratio of 1.5.

Then, as shown in FIGS. 4 and 6, the relationship between a refractiveindex n₂ and an extinction coefficient k₂ and a minimum film thickness dof an etching stopper film satisfying a front surface reflectioncontrast ratio of 1.5, and the relationship between a refractive indexn₂ and an extinction coefficient k₂ and a maximum film thickness d of anetching stopper film satisfying a transmittance of 80% were organized,respectively, and a configuration in which the respective conditions arecompatible was examined. As a result, it was found that the value of k₂satisfying the relationship

k ₂=−0.188×n ₂+0.879

when a maximum film thickness d is 3.0 nm and the value k₂ below suchvalue can make each condition of transmittance and contrast ratiocompatible (the same applies to the value of n₂, while k₂ was explainedherein for convenience). Namely, it was found that each condition oftransmittance and contrast ratio can be rendered compatible when arefractive index n₂ and an extinction coefficient k₂ of an etchingstopper film satisfy

k ₂≤−0.188×n ₂+0.879.  (Condition 1)

Further, in FIGS. 4 and 6, a region where

k ₂>−0.188×n ₂+0.879

is a region where a maximum film thickness d is less than 3.0 nm. On theother hand, in a region on the left side of the approximate curveindicated by d=3.0 nm (surface reflection contrast ratio 1.5) shown inFIGS. 4 and 6, a minimum film thickness d is a region exceeding 3.0 nm.Therefore, it was found that each condition cannot be made compatible inregions in FIGS. 4 and 6 where these regions overlap (hatched region B).In order to exclude this region, an intersection of an approximate curvehaving a minimum film thickness d=3.0 nm and the equation of(Condition 1) was calculated, and the approximate curve above theintersection was linearly approximated to obtain the following equation.

k ₂=2.750×n ₂−6.945

Namely, it was found that each condition of transmittance and contrastratio can be rendered compatible when a refractive index n₂ and anextinction coefficient k₂ of an etching stopper film satisfy

k ₂>−0.188×n ₂+0.879 and k ₂≤2.750×n ₂−6.945  (Condition 2)

This disclosure has been made as a result of the diligent studiesdescribed above. The approximate curves shown in FIGS. 4 to 7 varyslightly depending on calculation methods. However, the variation in theranges of a refractive index n₂ and an extinction coefficient k₂ causedby the above variation only slightly affects a contrast ratio, a filmthickness, and a transmittance of the etching stopper film, and iswithin an allowable range.

First Embodiment [Mask Blank and its Manufacture]

The embodiment is explained below with reference to the drawings.

A mask blank according to the first embodiment of this disclosure is amask blank used for manufacturing a CPL (Chromeless Phase Lithography)mask, namely, a chromeless phase shift mask. A CPL mask is a phase shiftmask of a type in which basically no light shielding film is provided ina transfer pattern forming region excluding a region of a large pattern,and a transfer pattern is formed by a dug-down portion and anon-dug-down portion of a transparent substrate.

FIG. 1 shows a configuration of a mask blank of the first embodiment. Amask blank 100 according to the first embodiment has an etching stopperfilm 2, a phase shift film 3, a light shielding film 4, and a hard maskfilm 5 on a main surface of a transparent substrate 1.

There is no particular limitation for the transparent substrate 1, aslong as the transparent substrate 1 has a high transmittance to anexposure light and sufficient rigidity. In this disclosure, a syntheticquartz glass substrate and other types of glass substrates (e.g.,soda-lime glass, aluminosilicate glass, etc.) can be used. Among thesesubstrates, a synthetic quartz glass substrate is particularlypreferable for the mask blank substrate of this disclosure used informing a high-fineness transfer pattern for having a high transmittanceto an ArF excimer laser light (193 nm wavelength) or at a region withshorter wavelength. The transparent substrate 1 preferably has arefractive index n₃ of 1.5 or more and 1.6 or less to a light of 193 nmwavelength, and an extinction coefficient k₃ of 0.1 or less to a lightof 193 nm wavelength. Incidentally, the lower limit of an extinctioncoefficient k₃ of the transparent substrate 1 is 0.0.

The etching stopper film 2 is made of a material that satisfies any ofthe aforementioned (Condition 1) and (Condition 2). The etching stopperfilm 2 is made of a material capable of obtaining an etching selectivitybetween the phase shift film 3 to dry etching using fluorine-based gaswhen patterning the phase shift film 3. The etching stopper film 2 isleft without being removed on the entire surface of a transfer patternforming region 101 when a phase shift mask 200 is completed (see FIG.2). Namely, the etching stopper film 2 remains even in a dug-downportion which is a region in the transparent portion without a phaseshift pattern 3 b. Therefore, the etching stopper film 2 is preferablyformed in contact with a main surface of the transparent substrate 1without any intervening film between the transparent substrate 1.

A transmittance of the etching stopper film 2 when a transmittance ofthe transparent substrate 1 to an exposure light is 100% is preferably80% or more, and more preferably 85% or more.

The etching stopper film 2 preferably has an oxygen content of 50 atom %or more. This is because the etching stopper film 2 is required tocontain a large amount of oxygen in order to make a transmittance to anexposure light equal to or greater than the aforementioned value. On theother hand, an oxygen content of the etching stopper film 2 ispreferably 67 atom % or less.

The etching stopper film 2 preferably includes a material containinghafnium and oxygen, in view of chemical durability and cleaningdurability. It is preferable that the etching stopper film 2 does notcontain an element which reduces an etching selectivity between thephase shift film 3 to dry etching using fluorine-based gas (e.g.,silicon). Further, the etching stopper film 2 is more preferably made ofa material including hafnium and oxygen. The material including hafniumand oxygen herein indicates a material containing, in addition to theseconstituent elements, only the elements inevitably contained in theetching stopper film 2 when the film is made by a sputtering method(noble gas such as helium (He), neon (Ne), argon (Ar), krypton (Kr), andxenon (Xe), hydrogen (H), carbon (C), etc.). By minimizing the presenceof other elements to be bonded to hafnium in the etching stopper film 2,the ratio of bonding of hafnium and oxygen in the etching stopper film 2can be significantly increased. Therefore, it is preferable that thetotal content of the aforementioned elements which are inevitablycontained in the etching stopper film 2 (noble gas, hydrogen, carbon,etc.) is 3 atom % or less. The etching stopper film 2 preferably has anamorphous structure. Thus, a surface roughness of the etching stopperfilm 2 can be improved, and a transmittance to an exposure light canalso be enhanced.

On the other hand, the etching stopper film 2 preferably contains notonly hafnium but also a metal element having an action to reduce anextinction coefficient k₂ of the etching stopper film 2, from theviewpoint of increasing a transmittance of the etching stopper film 2 toan ArF exposure light. From this point of view, aluminum, zirconium,indium, tin, etc. can be given as the metal elements to be contained inthe etching stopper film 2. For example, in forming the etching stopperfilm 2 from a material containing hafnium, aluminum, and oxygen, theratio of the content [atom %] of hafnium (Hf) to the total content [atom%] of hafnium (Hf) and aluminum (Al) (Hf/[Hf+Al] ratio) of the etchingstopper film 2 is preferably 0.86 or less. Hf/[Hf+Al] ratio of theetching stopper film 2 in such a case is preferably 0.60 or more.

The etching stopper film 2 preferably has a thickness of 1 nm or morebased on the premise of satisfying any of the aforementioned(Condition 1) and (Condition 2). Considering the influence of dryetching by fluorine-based gas and the influence of chemical cleaningperformed during manufacture of the phase shift mask from the maskblank, the thickness of the etching stopper film 2 is preferably 1 nm ormore. The thickness of the etching stopper film 2 is more preferably 2nm or more.

Although the etching stopper film 2 is made of a material having a hightransmittance to an exposure light, a transmittance decreases as thethickness increases. Further, the etching stopper film 2 has a higherrefractive index than the material forming the transparent substrate 1,and as the thickness of the etching stopper film 2 increases, theinfluence on designing a mask pattern to be actually formed in the phaseshift film 3 increases. Considering these points, the etching stopperfilm 2 is preferably 4 nm or less, and more preferably 3 nm or less.

A refractive index n₂ to a light of 193 nm wavelength of the etchingstopper film 2 is preferably 3.1 or less, and more preferably 3.0 orless. This is to reduce the influence on designing a mask pattern to beactually formed in the phase shift film 3. The etching stopper film 2 ismade at a refractive index n₂ of 2.6 or more. On the other hand, anextinction coefficient k₂ to a light of 193 nm wavelength (hereaftersimply referred to as extinction coefficient k₂) of the etching stopperfilm is preferably 0.4 or less. This is for enhancing a transmittance ofthe etching stopper film 2 to an exposure light or an inspection light.An extinction coefficient k₂ of the etching stopper film 2 is preferably0.05 or more, more preferably 0.1 or more, and even more preferably 0.2or more.

The etching stopper film 2 preferably has a high uniformity ofcomposition in the thickness direction (i.e., difference in contentamount of each constituent element in the thickness direction is withina variation width of 5 atom %). On the other hand, the etching stopperfilm 2 can be formed as a film structure with a composition gradient inthe thickness direction.

The phase shift film 3 includes a material containing silicon and oxygenthat is transparent to an exposure light, and has a predetermined phasedifference. Concretely, the phase shift film 3 of the transparentportion is patterned to form a non-dug-down portion where the phaseshift film 3 exists and a dug-down portion where the phase shift film 3does not exist, so as to achieve a relationship (predetermined phasedifference) in which the phase of an exposure light transmitted throughthe non-dug-down portion where the phase shift film 3 exists issubstantially inverted with respect to the exposure light (ArF excimerlaser exposure light) transmitted through the dug-down portion where thephase shift film 3 does not exist. In this way, the light beams whichhave come around each other's regions by a diffraction phenomenon canceleach other, so that the light intensity at the boundary is substantiallyzero and the resolution is improved.

The phase shift film 3 preferably has a function to transmit a light of193 nm wavelength with a transmittance of 95% or more (transmittance)and a function to generate a phase difference of 150 degrees or more and210 degrees or less between an exposure light transmitted through thephase shift film 3 and the light transmitted through the air by the samedistance as the thickness of the phase shift film 3. Further, the phasedifference in the phase shift film 3 is preferably 150 degrees or moreand 200 degrees or less, and more preferably 150 degrees or more and 190degrees or less. A transmittance of the phase shift film 3 to anexposure light is preferably 96% or more, and more preferably 97% ormore, in view of enhancing exposure efficiency.

The thickness of the phase shift film 3 is preferably 200 nm or less,and more preferably 190 nm or less. On the other hand, the thickness ofthe phase shift film 3 is preferably 143 nm or more, and more preferably153 nm or more.

For the phase shift film 3 to satisfy the conditions regarding theoptical properties and the film thickness mentioned above, a refractiveindex n₁ to a light of 193 nm wavelength is required to be 1.5 or more,more preferably 1.52 or more, and even more preferably 1.54 or more.Further, a refractive index n₁ of the phase shift film 3 is preferably1.68 or less, and more preferably 1.63 or less. An extinctioncoefficient k₁ to a light of 193 nm wavelength of the phase shift film 3is desired to be 0.1 or less, more preferably 0.02 or less, and evenmore preferably close to 0.

Incidentally, a refractive index n and an extinction coefficient k of athin film including the phase shift film 3 are not determined only bythe composition of the thin film. Film density and crystal condition ofthe thin film are also the factors that affect a refractive index n andan extinction coefficient k. Therefore, the conditions in forming a thinfilm by reactive sputtering are adjusted so that the thin film reachespredetermined refractive index n and extinction coefficient k. Informing the phase shift film 3 by reactive sputtering, for allowing arefractive index n₁ and an extinction coefficient k₁ to be within theabove range, it is effective to adjust the ratio of mixed gas of noblegas and reactive gas (oxygen gas). However, various other adjustmentsare made, such as pressure in a film forming chamber upon forming a filmby reactive sputtering, power applied to a sputtering target, andpositional relationship such as distance between a target and thetransparent substrate 1. Further, these film forming conditions areunique to film forming apparatuses which are adjusted arbitrarily sothat the phase shift film 3 to be formed reaches predeterminedrefractive index n₁ and extinction coefficient k₁.

While the phase shift film 3 can be configured from a single layer or astack of multiple layers, the phase shift film 3 includes a materialcontaining silicon and oxygen. By adding oxygen to silicon, hightransparency to an exposure light can be ensured, and preferable opticalcharacteristics as the phase shift film 3 can be obtained.

As mentioned above, the phase shift film 3 includes a materialcontaining silicon and oxygen. In order to enhance transmittance andlight fastness to an exposure light, and to enhance workability by dryetching, the phase shift film 3 preferably contains elements other thansilicon and oxygen of preferably 5 atom % or less, and more preferably 3atom % or less. More preferably, the phase shift film 3 is made of amaterial consisting of silicon and oxygen, such as SiO₂. In forming thephase shift film 3 by sputtering, noble gas such as helium (He), neon(Ne), argon (Ar), krypton (Kr), and xenon (Xe) used as buffer gas of thefilm, and hydrogen (H), carbon (C), etc. existing in a vacuum areinevitably contained. Even in that case, a total content of theseelements other than silicon and oxygen contained in the phase shift film3 is preferably set to 5 atom % or less, and more preferably 3 atom % orless, by optimizing the film forming conditions or performing annealingafter the film formation.

While the phase shift film 3 of a silicon oxide-based material is formedby sputtering, any sputtering method is applicable such as DCsputtering, RF sputtering, and ion beam sputtering. In the case wherethe target has a low conductivity (silicon target, SiO₂ target, etc.),it is preferable to apply RF sputtering and ion beam sputtering.Application of RF sputtering is preferable, considering the film formingrate.

A single layer structure and a stacked structure of two or more layersare applicable to the light shielding film 4. Further, each layer of thelight shielding film of a single layer structure and the light shieldingfilm with a stacked structure of two or more layers can be configured byapproximately the same composition in the thickness direction of thelayer or the film, or with a composition gradient in the thicknessdirection of the layer.

The light shielding film 4 is required to have a function of shieldingan exposure light with a high light shielding rate. The light shieldingfilm 4 is desired to ensure an optical density (OD) greater than 2.0,preferably 2.8 or more OD, and further preferably 3.0 or more OD. Asshown in FIG. 2, a light shielding band forming region 102 herein is alight shielding region formed outside a transfer pattern forming region101 where a pattern (circuit pattern) to be subjected to exposuretransfer is formed. The light shielding band forming region 102 is madefor the purpose of preventing adverse effects (overlapping of exposurelight) due to adjacent exposure upon exposure transfer to the wafer.

The mask blank 100 of the embodiment shown in FIG. 1 is configured bystacking the light shielding film 4 on the phase shift film 3 without anintervening film. For the light shielding film 4 of this configuration,it is necessary to apply a material having a sufficient etchingselectivity to etching gas used in forming a pattern in the phase shiftfilm 3. The light shielding film 4 in this case is preferably made of amaterial containing chromium. Materials containing chromium for formingthe light shielding film 4 can include, in addition to chromium metal, amaterial containing chromium and one or more elements selected fromoxygen, nitrogen, carbon, boron, and fluorine.

While a chromium-based material is generally etched by mixed gas ofchlorine-based gas and oxygen gas, an etching rate of the chromium metalto the etching gas is not as high. Considering enhancing an etching rateof mixed gas of chlorine-based gas and oxygen gas to etching gas, thematerial forming the light shielding film 4 preferably contains chromiumand one or more elements selected from oxygen, nitrogen, carbon, boron,and fluorine. Further, one or more elements among molybdenum, indium,and tin can be included in the material containing chromium for formingthe light shielding film 4. Including one or more elements amongmolybdenum, indium, and tin can increase an etching rate to mixed gas ofchlorine-based gas and oxygen gas.

In the mask blank 100, a preferable configuration is that the lightshielding film 4 has further stacked thereon a hard mask film 5 made ofa material having an etching selectivity to etching gas used in etchingthe light shielding film 4. Since the hard mask film 5 is basically notrestricted by an optical density, the thickness of the hard mask film 5can be reduced significantly compared to the thickness of the lightshielding film 4. A resist film of an organic material only requires afilm thickness to function as an etching mask until dry etching forforming a pattern in the hard mask film 5 is completed. Therefore, thethickness of the resist film can be reduced significantly compared toconventional cases. Reduction of the film thickness of a resist film iseffective for enhancing resist resolution and preventing collapse ofpattern, which is extremely important in facing the requirements forminiaturization.

In the case where the light shielding film 4 is made of a materialcontaining chromium, the hard mask film 5 is preferably made of amaterial containing silicon. The hard mask film 5 in this case tends tohave low adhesiveness with a resist film of an organic material.Therefore, it is preferable to treat the surface of the hard mask film 5with HMDS (Hexamethyldisilazane) to enhance surface adhesiveness. Thehard mask film 5 in this case is more preferably made of SiO₂, SiN,SiON, etc.

Further, in the case where the light shielding film is made of amaterial containing chromium, the materials containing tantalum are alsoapplicable as the materials of the hard mask film 5, in addition to thematerial containing silicon given above. The material containingtantalum in this case includes, in addition to tantalum metal, amaterial containing tantalum and one or more elements selected fromnitrogen, oxygen, boron, and carbon.

On the other hand, the light shielding film 4 can have a structure wherea layer including a material containing chromium and a layer including amaterial containing a transition metal and silicon are stacked, in thisorder, from the phase shift film 3 side. Concrete matters on thematerial containing chromium in this case are similar to the case of thelight shielding film 4 described above. The transition metal to beincluded in the layer including a material containing a transition metaland silicon includes one metal among molybdenum (Mo), tantalum (Ta),tungsten (W), titanium (Ti), chromium (Cr), hafnium (Hf), nickel (Ni),vanadium (V), zirconium (Zr), ruthenium (Ru), rhodium (Rh), zinc (Zn),niobium (Nb), palladium (Pd), etc., or an alloy of these metals. Metalelements other than the transition metal elements to be included in thelayer include aluminum (Al), indium (In), tin (Sn), gallium (Ga), etc.

In the case where the light shielding film 4 has a structure where alayer including a material containing chromium and a layer including amaterial containing a transition metal and silicon are stacked asmentioned above, the hard mask film 5 is preferably made of a materialcontaining chromium.

In the mask blank 100, a resist film of an organic material ispreferably formed in contact with the surface of the hard mask film 5 atthe film thickness of 100 nm or less. In the case of a fine pattern tomeet DRAM hp32 nm generation, a SRAF (Sub-Resolution Assist Feature)with 40 nm line width may be provided on a transfer pattern (phase shiftpattern) to be formed in the hard mask film 5. Even in this case,cross-sectional aspect ratio of the resist pattern can be reduced downto 1:2.5 so that collapse and peeling off of the resist pattern can beprevented in rinsing, developing of the resist film, etc. Incidentally,the resist film preferably has a film thickness of 80 nm or less, sincecollapse and peeling off of the resist pattern can further be prevented.

While the etching stopper film 2, the phase shift film 3, the lightshielding film 4, and the hard mask film 5 are formed by sputtering, anysputtering method is applicable such as DC sputtering, RF sputtering,and ion beam sputtering. In the case where the target has a lowconductivity, application of RF sputtering and ion beam sputtering ispreferable. Application of RF sputtering is more preferable, consideringthe film forming rate.

In the method of forming the etching stopper film 2, it is preferable toarrange a target containing hafnium (hafnium target substantially freeof oxygen excluding surface layer or target containing hafnium andoxygen) in a film forming chamber to form the etching stopper film 2 onthe transparent substrate 1. Concretely, the transparent substrate 1 isplaced on a substrate stage in a film forming chamber, and apredetermined voltage is applied (preferably RF power source in thiscase) to the target under a noble gas atmosphere such as argon gas (ormixed gas atmosphere of oxygen gas or oxygen-containing gas). As aresult, a sputtering phenomenon occurs due to collision of plasmarizednoble gas particles with the target, and the etching stopper film 2containing hafnium and oxygen is formed on the surface of thetransparent substrate 1. In this circumstance, the film formingcondition is set so that a film thickness, a refractive index n₂, and anextinction coefficient k₂ of the etching stopper film 2 satisfy any ofthe aforementioned (Condition 1) and (Condition 2).

As described above, in the mask blank 100 of the first embodiment, themask blank 100 for a phase shift mask can be provided, which includesthe etching stopper film 2 with a high transmittance to an ArF exposurelight and which can obtain a high contrast ratio to an inspection lightof 193 nm wavelength that is equivalent to that of an ArF exposurelight.

[Phase Shift Mask and its Manufacture]

A phase shift mask 200 (see FIG. 2) of the first embodiment is featuredin that the etching stopper film 2 of the mask blank 100 is left on theentire main surface of the transparent substrate 1, a phase shiftpattern 3 a is formed in the phase shift film 3, and a light shieldingpattern 4 b is formed in the light shielding film 4. Incidentally, thehard mask film 5 is removed during manufacture of the phase shift mask200 (see FIGS. 3A-3G).

Namely, the phase shift mask 200 according to the first embodiment has astructure where the transparent substrate 1 has stacked thereon theetching stopper film 2, the phase shift pattern 3 a, and the lightshielding pattern 4 b in this order. The phase shift pattern 3 aincludes material containing silicon and oxygen. The etching stopperfilm 2 is featured in being made of a material that satisfies any of theaforementioned (Condition 1) and (Condition 2). The etching stopper film2 is made of a material capable of obtaining an etching selectivitybetween the phase shift film 3 to dry etching using fluorine-based gaswhen patterning the phase shift film 3. Concrete configurations of thetransparent substrate 1, the etching stopper film 2, the phase shiftpattern 3 a, and the light shielding pattern 4 b of the phase shift mask200 are similar to the mask blank 100.

The method for manufacturing the phase shift mask 200 of the firstembodiment is explained below according to the manufacturing steps shownin FIGS. 3A-3G show a cross-sectional structure of a major portion.Described herein is the case where a material containing chromium isapplied to the light shielding film 4, and a material containing siliconis applied to the hard mask film 5.

First, a resist film is formed in contact with the hard mask film 5 ofthe mask blank 100 by spin coating. Next, a pattern to be formed in thephase shift film 3 is written on the resist film with an electron beam,and predetermined treatments such as developing are further conducted tothereby form a first resist pattern 6 a (see FIG. 3A). Subsequently, dryetching is conducted using fluorine-based gas with the first resistpattern 6 a as a mask, and a hard mask pattern 5 a is formed in the hardmask film 5 (see FIG. 3B).

Next, the first resist pattern 6 a is removed. Next, dry etching iscarried out using mixed gas of chlorine-based gas and oxygen-based gaswith the hard mask pattern 5 a as a mask, and a light shielding pattern4 a is formed in the light shielding film 4 (see FIG. 3C). Subsequently,dry etching is carried out using fluorine-based gas with the lightshielding pattern 4 a as a mask, and a phase shift pattern 3 a is formedin the phase shift film 3 (see FIG. 3D). The hard mask pattern 5 a isremoved by this dry etching.

Next, a resist film is formed by spin coating. Thereafter, a patternwhich should be formed in the light shielding film 4 (pattern includinglight shielding band) is written with an electron beam on the resistfilm, and predetermined treatments such as developing are furtherconducted, to thereby form a second resist pattern 7 b (see FIG. 3E).

Next, dry etching is carried out using mixed gas of chlorine-based gasand oxygen gas with the second resist pattern 7 b as a mask, and a lightshielding pattern 4 b is formed in the light shielding film 4 (see FIG.3F).

Thereafter, the second resist pattern 7 b is removed and moves on to acleaning step. After the cleaning step, a mask defect inspection isperformed as necessary using a light of 193 nm wavelength. Further,depending on the result of the defect inspection, a defect repair iscarried out as necessary and the phase shift mask 200 is manufactured(see FIG. 3G). The etching stopper film 2 has a high transmittance to anArF exposure light of 193 nm wavelength and can obtain a high contrastratio to an inspection light of 193 nm wavelength that is equivalent tothat of the ArF exposure light. Therefore, defect inspection and defectrepair can be made at a high precision.

[Manufacture of Semiconductor Device]

The method of manufacturing a semiconductor device according to thefirst embodiment is featured in that a transfer pattern isexpose-transferred to a resist film on a semiconductor substrate usingthe phase shift mask 200 of the first embodiment or the phase shift mask200 manufactured by using the mask blank 100 of the first embodiment.Therefore, when an exposure transfer is made on a resist film on asemiconductor device using the phase shift mask 200 of the firstembodiment, a pattern can be formed in the resist film on thesemiconductor device at a precision sufficiently satisfying the designspecification.

A description has been given in the foregoing on an embodiment in whichthe mask blank 100 of the first embodiment is applied to manufacture aCPL mask. However, the mask blank of this disclosure is not particularlylimited to the CPL mask, and can similarly be applied for manufacturinga Levenson type phase shift mask, for example.

Example 1

The embodiment of this disclosure is described in greater detail belowtogether with examples.

Example 1 [Manufacture of Mask Blank]

A transparent substrate 1 including a synthetic quartz glass with a sizeof a main surface of about 152 mm×about 152 mm and a thickness of about6.35 mm was prepared. An end surface and the main surface of thetransparent substrate 1 were polished to a predetermined surfaceroughness or less (0.2 nm or less root mean square roughness Rq), andthereafter subjected to predetermined cleaning treatment and dryingtreatment. Each optical characteristic of the transparent substrate 1was measured using a spectroscopic ellipsometer (M-2000D manufactured byJ.A. Woollam), and a refractive index n₃ was 1.556 and an extinctioncoefficient k₃ was 0.00 (lower measurement limit) to a light of 193 nmwavelength.

Next, an etching stopper film 2 including hafnium and oxygen (HfO film)was formed in contact with a surface of the transparent substrate 1 at athickness of 3 nm. Concretely, the etching stopper film 2 was formed byplacing the transparent substrate 1 in a single-wafer RF sputteringapparatus, discharging a Hf target, and by sputtering (RF sputtering)using mixed gas of argon (Ar) and oxygen (O₂) as sputtering gas. Anetching stopper film formed on another transparent substrate under thesame conditions was analyzed by X-ray photoelectron spectroscopy, andthe result was Hf:O=34:66 (atom % ratio).

Further, each optical characteristic of the etching stopper film 2 wasmeasured using the spectroscopic ellipsometer (M-2000D manufactured byJ.A. Woollam), and a refractive index n₂ was 2.73 and an extinctioncoefficient k₂ was 0.36 in a light of 193 nm wavelength.

Next, a phase shift film 3 including SiO₂ containing silicon and oxygenwas formed in contact with a surface of the etching stopper film 2 at athickness of 177 nm. Concretely, the transparent substrate 1 having theetching stopper film 2 formed thereon was placed in a single-wafer RFsputtering apparatus, and by RF sputtering using a silicon dioxide(SiO₂) target and argon (Ar) gas as sputtering gas, a phase shift film 3including SiO₂ was formed on the etching stopper film 2. Incidentally,on a main surface of another transparent substrate 1, only a phase shiftfilm 3 including SiO₂ was formed under the same condition, opticalcharacteristics of the uppermost layer were measured using thespectroscopic ellipsometer, and a refractive index n₁ was 1.56 and anextinction coefficient k₁ was 0.00 (lower measurement limit) in a lightof 193 nm wavelength.

Next, a light shielding film 4 containing chromium was formed in contactwith a surface of the phase shift film 3 at a thickness of 59 nm. Thelight shielding film 4 is a CrOC film containing oxygen and carbon inaddition to chromium. Concretely, the transparent substrate 1 having thephase shift film 3 formed thereon was placed in a single-wafer DCsputtering apparatus, and by reactive sputtering (DC sputtering) using achromium (Cr) target under a mixed gas atmosphere of carbon dioxide(CO₂) and helium (He), a light shielding film 4 was formed. Next, thetransparent substrate 1 having the light shielding film 4 (CrOC film)formed thereon was subjected to heat treatment. Concretely, the heattreatment was carried out using a hot plate at a heating temperature of280° C. in the atmosphere for five minutes.

The light shielding film 4 after the heat treatment was analyzed byX-ray photoelectron spectroscopy (ESCA with RBS correction). As aresult, it was confirmed that the region near the surface that isopposite to the transparent substrate 1 side of the light shielding film(region up to about 2 nm depth from the surface) has a compositiongradient portion having more oxygen content than other regions (40 atom% or more oxygen content). Further, content of each constituent elementin the region of the light shielding film 4 excluding the compositiongradient portion was found to be, at an average value, Cr:71 atom %,0:15 atom %, and C:14 atom %. Moreover, it was confirmed that eachdifference of each constituent element in thickness direction of theregion of the light shielding film 4 excluding the composition gradientportion is 3 atom % or less, and there is substantially no compositiongradient in thickness direction. Incidentally, the compositions of otherfilms shown below were also obtained by X-ray photoelectron spectroscopy(ESCA with RBS correction) similar to the light shielding film 4.

A spectrophotometer (Cary4000 manufactured by Agilent Technologies) wasused on the light shielding film 4 after the heat treatment to measurean optical density (OD) to an ArF excimer laser light wavelength (about193 nm), confirming the value of 3.0 or more.

Next, a hard mask film 5 including SiO₂ containing silicon and oxygenwas formed in contact with a surface of the light shielding film 4 at athickness of 12 nm. Concretely, the transparent substrate 1 having thelight shielding film 4 formed thereon was placed in a single-wafer RFsputtering apparatus, and by RF sputtering using silicon dioxide (SiO₂)target and argon (Ar) gas as sputtering gas, a hard mask film 5including SiO₂ was formed on the light shielding film 4. A mask blank100 of Example 1 was manufactured through the above procedure.

Incidentally, an etching stopper film was formed on another transparentsubstrate through the same procedure, and a front surface reflectance(reflectance on the side opposite the transparent substrate 1) and aback surface reflectance (reflectance of the transparent substrate 1side) in a light of 193 nm wavelength with the etching stopper filmalone were measured respectively by the spectroscopic ellipsometer. As aresult, a front surface reflectance was 14.3%, and a back surfacereflectance was 10.7%.

Subsequently, a phase shift film 3 was formed in contact with a surfaceof the etching stopper film 2 through the same procedure, and a frontsurface reflectance (reflectance on the side opposite the transparentsubstrate 1) and a back surface reflectance (reflectance of thetransparent substrate 1 side) in a light of 193 nm wavelength of astacked structure of the etching stopper film 2 and the phase shift film3 were measured respectively by the spectroscopic ellipsometer. As aresult, a transmittance was 81.3% when a transmittance of thetransparent substrate 1 was 100%, a front surface reflectance was 9.0%,and a back surface reflectance was 6.2%.

From this result, it was found that an influence of reduction intransmittance caused by providing the etching stopper film 2 of Example1 is small. On the other hand, a contrast ratio calculated by dividing afront surface reflectance of the etching stopper film 2 alone by a frontsurface reflectance of a stacked structure of the etching stopper film 2and the phase shift film 3 was 1.59. On the other hand, a contrast ratiocalculated by dividing a back surface reflectance of the etching stopperfilm 2 alone by a back surface reflectance of a stacked structure of theetching stopper film 2 and the phase shift film 3 was 1.73. Bothcontrast ratios are 1.5 or more. Therefore, even if the phase shift mask200 was manufactured from the mask blank 100 of Example 1 and a maskdefect was inspected on the phase shift mask 200 by a mask inspectionapparatus where a light of 193 nm wavelength is used as an inspectionlight, the mask defect can be evaluated normally.

[Manufacture and Evaluation of Phase Shift Mask]

Next, a phase shift mask 200 of Example 1 was manufactured through thefollowing procedure using the mask blank 100 of Example 1. First, asurface of a hard mask film 5 was subjected to HMDS treatment.Subsequently, a resist film of a chemically amplified resist forelectron beam writing was formed in contact with a surface of the hardmask film 5 by spin coating at a film thickness of 80 nm. Next, apattern to be formed in the phase shift film 3 was written on the resistfilm by an electron beam, and a predetermined development treatment wasconducted to thereby form a first resist pattern 6 a (see FIG. 3A). Atthis stage, a program defect was added to the first resist pattern 6 ain addition to the phase shift pattern that is to be originally formedso that a defect is formed on the phase shift film 3.

Next, dry etching using CF₄ gas was conducted with the first resistpattern 6 a as a mask, and a hard mask pattern 5 a was formed in thehard mask film 5 (see FIG. 3B).

Next, the remaining first resist pattern 6 a was removed by TMAH.Subsequently, dry etching was conducted under a high bias conditionusing mixed gas of chlorine and oxygen (gas flow ratio Cl₂:O₂=20:1) withthe hard mask pattern 5 a as a mask, and a light shielding pattern 4 awas formed in the light shielding film 4 (see FIG. 3C).

Subsequently, dry etching was conducted using CF₄ gas with the lightshielding pattern 4 a as a mask, and a phase shift pattern 3 a wasformed in the phase shift film 3 (see FIG. 3D). At the initial stage ofthis etching, the hard mask pattern 5 a formed on the light shieldingpattern 4 a also functioned as an etching mask. However, since thematerial of the hard mask film 5 and the material of the phase shiftfilm 3 are similarly SiO₂, the hard mask pattern 5 a was removed at anearly stage.

Next, a resist film of a chemically amplified resist for electron beamwriting was formed in contact with a surface of the light shieldingpattern 4 a by spin coating at a film thickness of 200 nm. Next, apattern to be formed in the light shielding film 4 was written on theresist film by an electron beam, and a predetermined developmenttreatment was conducted to thereby form a second resist pattern 7 b (seeFIG. 3E). Subsequently, dry etching was conducted using mixed gas ofchlorine and oxygen (gas flow ratio Cl₂:O₂=4:1) with the second resistpattern 7 b as a mask, and a light shielding pattern 4 b was formed inthe light shielding film 4 (see FIG. 3F). Next, the second resistpattern 7 b was removed by ashing, subjected to cleaning treatment, andthe phase shift mask (CPL mask) 200 of Example 1 was manufactured (seeFIG. 3G).

The manufactured phase shift mask 200 of Example 1 was subjected to amask pattern inspection by a mask inspection apparatus (Teron640manufactured by KLA-Tencor) in which a light of 193 nm wavelength isused as an inspection light. As a result, a defect was detected on thephase shift pattern 3 a of a location where a program defect wasarranged.

On the phase shift mask 200 of Example 1, a simulation of a transferimage was made when an exposure transfer was made on a resist film on asemiconductor device at an exposure light of 193 nm wavelength, usingAIMS193 (manufactured by Carl Zeiss). The simulated exposure transferimage was inspected, and the design specification was fully satisfiedexcept for the location where the program defect exists. There waslittle influence on the exposure transfer caused by the reduction oftransmittance of the transparent portion by providing the etchingstopper film 2. It can be considered from this result that a circuitpattern to be finally formed on the semiconductor device can be formedat a high precision, even if the phase shift mask 200 of Example 1 wasset on a mask stage of an exposure apparatus and a resist film on thesemiconductor device was subjected to exposure transfer.

Example 2 [Manufacture of Mask Blank]

A mask blank 100 of Example 2 was manufactured through the sameprocedure as the mask blank 100 of Example 1, except for theconfiguration of the etching stopper film 2. Concretely, in the maskblank 100 of Example 2, the etching stopper film 2 was made from amaterial having a refractive index n₂ of 2.70 and an extinctioncoefficient k₂ of 0.40 in a light of 193 nm wavelength, with a filmthickness of 2.8 nm. Therefore, the structure of the mask blank 100having the etching stopper film 2, the phase shift film 3, and the lightshielding film 4 stacked in this order on the transparent substrate 1,and the materials and manufacturing methods of the transparent substrate1, the phase shift film 3, and the light shielding film 4 are the sameas those of Example 1.

A transmittance of a light of 193 nm wavelength in a stacked state ofthe etching stopper film 2 and the phase shift film 3 of Example 2 wasmeasured in the same manner as in Example 1, and the transmittance was80.1% when a transmittance of the transparent substrate 1 was 100%. Fromthis result, it was found that the influence of reduction intransmittance caused by providing the etching stopper film 2 of Example2 is small. On the other hand, a contrast ratio calculated through thesame procedure as Example 1 by dividing a front surface reflectance ofthe etching stopper film 2 of Example 2 alone by a front surfacereflectance of a stacked structure of the etching stopper film 2 and thephase shift film 3 was 1.50. On the other hand, a contrast ratiocalculated by dividing a back surface reflectance of the etching stopperfilm 2 of Example 2 alone by a back surface reflectance of a stackedstructure of the etching stopper film 2 and the phase shift film 3 was1.60. Both contrast ratios are 1.5 or more. Therefore, even if the phaseshift mask 200 was manufactured from the mask blank 100 of Example 2 anda mask defect was inspected on the phase shift mask 200 by a maskinspection apparatus where a light of 193 nm wavelength is used as aninspection light, the mask defect can be evaluated normally.

[Manufacture and Evaluation of Phase Shift Mask]

Next, a phase shift mask 200 of Example 2 was manufactured using themask blank 100 of Example 2 through the same procedure as Example 1. Themanufactured phase shift mask 200 of Example 2 was subjected to a maskpattern inspection by a mask inspection apparatus (Teron640 manufacturedby KLA-Tencor) in which a light of 193 nm wavelength is used as aninspection light. As a result, a defect was detected on the phase shiftpattern 3 a of a location where a program defect was arranged.

On the phase shift mask 200 of Example 2, a simulation of a transferimage was made when an exposure transfer was made on a resist film on asemiconductor device at an exposure light of 193 nm wavelength, usingAIMS193 (manufactured by Carl Zeiss). The simulated exposure transferimage was inspected, and the design specification was fully satisfiedexcept for the location where the program defect exists. There waslittle influence on the exposure transfer caused by reduction oftransmittance of the transparent portion by providing the etchingstopper film 2. It can be considered from this result that a circuitpattern to be finally formed on the semiconductor device can be formedat a high precision, even if the phase shift mask 200 of Example 2 wasset on a mask stage of an exposure apparatus and a resist film on thesemiconductor device was subjected to exposure transfer.

Comparative Example 1 [Manufacture of Mask Blank]

The mask blank of Comparative Example 1 was manufactured through thesame procedure as the mask blank 100 of Example 1, except for theconfiguration of the etching stopper film. Concretely, in the mask blankof Comparative Example 1, the etching stopper film was made from amaterial having a refractive index n₂ of 2.60 and an extinctioncoefficient k₂ of 0.40 in a light of 193 nm wavelength, with a filmthickness of 2.9 nm. Therefore, the structure of the mask blank havingthe etching stopper film, the phase shift film, and the light shieldingfilm stacked in this order on the transparent substrate, and thematerials and manufacturing methods of the transparent substrate, thephase shift film, and the light shielding film are the same as those ofExample 1.

A transmittance of a light of 193 nm wavelength in the stacked state ofthe etching stopper film and the phase shift film of Comparative Example1 was measured in the same manner as in Example 1, and the transmittancewas 80.1% when a transmittance of the transparent substrate was 100%.However, a contrast ratio calculated through the same procedure asExample 1 by dividing a front surface reflectance of the etching stopperfilm of Comparative Example 1 alone by a front surface reflectance of astacked structure of the etching stopper film and the phase shift filmwas 1.46, which is below 1.50. Therefore, when the phase shift mask wasmanufactured from the mask blank of Comparative Example 1 and a maskdefect was inspected on the phase shift mask by a mask inspectionapparatus where a light of 193 nm wavelength is used as an inspectionlight, it is considered as difficult to evaluate the mask defectnormally.

[Manufacture and Evaluation of Phase Shift Mask]

Next, using the mask blank of Comparative Example 1, a phase shift maskof Comparative Example 1 was manufactured through the same procedure asExample 1. The manufactured phase shift mask of Comparative Example 1was subjected to a mask pattern inspection by a mask inspectionapparatus (Teron640 manufactured by KLA-Tencor) in which a light of 193nm wavelength is used as an inspection light. As a result, a defectcould not be detected on the phase shift pattern in a location where aprogram defect was arranged.

On the phase shift mask of Comparative Example 1, a simulation of atransfer image was made when an exposure transfer was made on a resistfilm on a semiconductor device at an exposure light of 193 nmwavelength, using AIMS193 (manufactured by Carl Zeiss). The simulatedexposure transfer image was inspected, and the design specification wasfully satisfied except for the location where the program defect exists.However, since the phase shift mask of Comparative Example 1 cannotdetect a program defect, the defect portion cannot be repaired. It canbe understood from this result that when the phase shift mask ofComparative Example 1 was set on a mask stage of an exposure apparatusand exposure-transferred on a resist film on a semiconductor device,frequent generation of short-circuit or disconnection is expected on acircuit pattern to be finally formed on the semiconductor device.

DESCRIPTION OF REFERENCE NUMERALS

-   1. transparent substrate-   2. etching stopper film-   3. phase shift film-   3 a. phase shift pattern-   4. light shielding film-   4 a, 4 b light shielding pattern-   5. hard mask film-   5 a. hard mask pattern-   6 a. first resist pattern-   7 b. second resist pattern-   100. mask blank-   200. phase shift mask-   101. transfer pattern forming region-   102. light shielding band forming region

1. A mask blank, comprising: a transparent substrate; an etching stopperfilm provided on the transparent substrate; and a phase shift filmprovided on the etching stopper film and containing silicon and oxygen,wherein a refractive index n₁ of the phase shift film for light of 193nm wavelength is 1.5 or more and an extinction coefficient k₁ of thephase shift film for light of 193 nm wavelength is 0.1 or less, andwherein a refractive index n₂ of the etching stopper film for light of193 nm wavelength is 2.6 or more and an extinction coefficient k₂ of theetching stopper film for light of 193 nm wavelength is 0.4 or less, andwherein the refractive index n₂ and the extinction coefficient k₂ of theetching stopper film satisfy at least one of the following twoconditions:k ₂≤[(−0.188×n ₂)+0.879];  (Condition 1)k ₂≤[(2.750×n ₂)−6.945].  (Condition 2)
 2. The mask blank according toclaim 1, wherein the refractive index n₂ of the etching stopper film is3.1 or less.
 3. The mask blank according to claim 1, wherein theextinction coefficient k₂ of the etching stopper film is 0.05 or more.4. The mask blank according to claim 1, wherein the refractive index n₁of the phase shift film is 1.6 or less.
 5. The mask blank according toclaim 1, wherein a refractive index n₃ of the transparent substrate forlight of 193 nm wavelength is 1.5 or more and 1.6 or less, and anextinction coefficient k₃ of the transparent substrate for light of 193nm wavelength is 0.1 or less.
 6. The mask blank according to claim 1,wherein a stack comprising the etching stopper film and the phase shiftfilm has a transmittance of 80% or more for light of 193 nm wavelength.7. The mask blank according to claim 1, wherein, for light of 193 nmwavelength, a contrast ratio of a front surface reflectance of theetching stopper film alone to a front surface reflectance of a stackcomprising the etching stopper film and the phase shift film is 1.5 ormore.
 8. The mask blank according to claim 1, wherein the etchingstopper film contains hafnium and oxygen.
 9. The mask blank according toclaim 1, wherein the etching stopper film is formed in contact with amain surface of the transparent substrate.
 10. The mask blank accordingto claim 1, wherein the etching stopper film has a thickness of 1 nm ormore and 4 nm or less.
 11. The mask blank according to claim 1, whereinthe phase shift film is configured to generate a phase difference of 150degrees or more and 210 degrees or less between light of 193 nmwavelength transmitted through the phase shift film and light of 193 nmwavelength transmitted through air for a same distance as a thickness ofthe phase shift film.
 12. The mask blank according to claim 1 comprisinga light shielding film on the phase shift film.
 13. The mask blankaccording to claim 12, wherein the light shielding film containschromium.
 14. A phase shift mask, comprising: a transparent substrate;an etching stopper film provided on the transparent substrate; and aphase shift film provided on the etching stopper film, containingsilicon and oxygen, and having a phase shift pattern, wherein arefractive index n₁ of the phase shift film for light of 193 nmwavelength is 1.5 or more and an extinction coefficient k₁ of the phaseshift film for light of 193 nm wavelength is 0.1 or less, and wherein arefractive index n₂ of the etching stopper film for light of 193 nmwavelength is 2.6 or more and an extinction coefficient k₂ of theetching stopper film for light of 193 nm wavelength is 0.4 or less, andwherein the refractive index n₂ and the extinction coefficient k₂ of theetching stopper film satisfy at least one of the following twoconditions:k ₂≤[(−0.188×n ₂)+0.879];  (Condition 1)k ₂≤[(2.750×n ₂)−6.945].  (Condition 2)
 15. The phase shift maskaccording to claim 14, wherein the refractive index n₂ of the etchingstopper film 3.1 or less.
 16. The phase shift mask according to claim14, wherein the extinction coefficient k₂ of the etching stopper film is0.05 or more.
 17. The phase shift mask according to claim 14, whereinthe refractive index n₁ of the phase shift film is 1.6 or less.
 18. Thephase shift mask according to claim 14, wherein a refractive index n₃ ofthe transparent substrate for light of 193 nm wavelength is 1.5 or moreand 1.6 or less, and an extinction coefficient k₃ of the transparentsubstrate for light of 193 nm wavelength is 0.1 or less.
 19. The phaseshift mask according to claim 14, wherein a stack comprising the etchingstopper film and the phase shift film has a transmittance of 80% or morefor light of 193 nm wavelength.
 20. The phase shift mask according toclaim 14, wherein, for light of 193 nm wavelength, a contrast ratio of afront surface reflectance of the etching stopper film alone to a frontsurface reflectance of stack comprising the etching stopper film and thephase shift film is 1.5 or more.
 21. The phase shift mask according toclaim 14, wherein the etching stopper film contains hafnium and oxygen.22. The phase shift mask according to claim 14, wherein the etchingstopper film is formed in contact with a main surface of the transparentsubstrate.
 23. The phase shift mask according to claim 14, wherein theetching stopper film has a thickness of 1 nm or more and 4 nm or less.24. The phase shift mask according to claim 14, wherein the phase shiftfilm is configured to generate a phase difference of 150 degrees or moreand 210 degrees or less between light of 193 nm wavelength transmittedthrough the phase shift film and light of 193 nm wavelength transmittedthrough air for a same distance as a thickness of the phase shift film.25. The phase shift mask according to claim 14 comprising a lightshielding film having a light shielding pattern with a light shieldingband on the phase shift film.
 26. The phase shift mask according toclaim 25, wherein the light shielding film contains chromium.
 27. Amethod of manufacturing a semiconductor device comprisingexposure-transferring a pattern on the phase shift mask according toclaim 14 to a resist film on a semiconductor substrate.